1. Field of the Invention
The present invention relates to an optical connector, and more particularly, to an optical connector that employs a guide-pin positioning method, such as an MT optical connector stipulated in Japanese Industrial Standard (JIS) C 5981.
2. Description of the Related Art
MT optical connectors stipulated in JIS C 5981 employ the guide-pin positioning method to provide precise positioning and butt connection. FIG. 1A shows the structure of an MT optical connector. A ferrule 11 has a pair of guide holes 12 opening at an end face 11a and optical fiber holes 13 disposed between the pair of guide holes 12.
A pair of guide pins 14 is inserted and fitted into the guide holes 12 of one ferrule 11 so as to protrude from the end face 11a, as shown in FIG. 1A. These protruding guide pins 14 are inserted and fitted into the guide holes 12 of the other ferrule 11, and the end faces 11a of the pair of ferrules 11 are butted against each other. Then, optical fibers 15 accommodated and precisely positioned in the optical fiber holes 13 are butted against each other and connected at the end faces 11a of both ferrules 11.
A clamp spring 16 made of a leaf spring member is mounted so as to sandwich the pair of ferrules 11. With this, the end faces 11a of the pair of ferrules 11 are pushed against each other with a predetermined pushing force. FIG. 1B shows a state in which the clamp spring 16 has been mounted and the optical connector connection has been completed. In FIGS. 1A and 1B, optical fiber tapes 17 are formed by bonding a plurality of (for example, eight) optical fibers (optical fiber core wires) 15 to each other with a resin to unite them. The ferrules 11 are mounted to ends of the optical fiber tapes 17.
FIG. 2 shows the structure of an optical connector described in Japanese Patent Application Laid Open No. 2004-45966 (hereafter called Literature 1). The structure of this optical connector conforms to that of MT optical connectors stipulated in JIS C 5981. Components corresponding to those shown in FIG. 1A are assigned the same symbols as those in FIG. 1A.
The optical connector shown in FIG. 2 has escape faces 11b at end faces 11a of a pair of ferrules 11 that are butted against each other. The escape faces 11b are curved surfaces and are formed in all portions except for a portion where optical fiber holes (not shown) are formed (around the portion where the optical fiber holes are formed). Guide holes 12 open at the escape faces 11b. 
If foreign matter such as dirt or dust gets stuck on the end faces 11a of the ferrules 11, the connection loss increases when the ferrules 11 are butted against each other for connection. Therefore, foreign matter should be cleared or removed. Foreign matter that gets stuck around the guide pins 14 may remain because it is difficult to remove it due to the positions of the guide pins 14.
The optical connector shown in FIG. 2 copes with this difficulty well. Since the guide holes 12 open at the escape faces 11b, even if foreign matter 21 such as dirt or dust remains around the guide pins 14, as shown in FIG. 2, the foreign mater 21 does not affect the connection. Portions where the optical fibers are disposed can be butted against each other to be connected without any gap between the end faces 11a of the ferrules 11.
MT optical connectors shown in FIGS. 1A and 1B have been used conventionally for trunk line systems such as public communication line networks. In recent years, MT optical connectors have come to be used for signal connections between electronic units that use optical signals. The range of applications has expanded.
When MT optical connectors are used in a trunk line system, basically, repeated connection and disconnection of the MT optical connectors hardly occur. It is easily expected, however, that connection and disconnection of MT optical connectors are frequently repeated in general electric consumer appliance fields for connecting electronic devices.
Assuming that the connection and disconnection of MT optical connectors conforming to JIS C 5981 are frequently repeated, changes in connection loss that occurred as a result of repeated connection and disconnection were examined. In JIS C 5981, the guide hole diameter and the guide pin diameter of MT optical connectors are stipulated as follows:                Guide hole diameter: 0.700±0.001 mm        Guide pin diameter: 0.698±0.001 mm        
In a connection and disconnection test, the diameters of the guide holes of ferrules to be used and the diameters of guide pins were measured. A pair of ferrules having a guide hole diameter of 0.700 mm and two guide pins having a diameter of 0.698 mm were used in the test. A clamp spring connection method was used and the number of times the ferrules were connected and disconnected was set to 2,000.
FIG. 3 shows the results of the connection and disconnection test. The connection loss was not constant and frequently increased (worsened). Every time the connection loss increased, the end faces 11a of the ferrules 11 were cleaned, and then the test was continued.
It is understood from FIG. 3 that the connection loss increased about once every 100 connections and disconnections. It is also understood that a very large connection loss which may impair the connection performance sometimes occurred suddenly.
The reason why such changes in connection loss occurred was checked, and it was found that powder caused by the friction generated when the guide pins were inserted and fitted into the guide holes got stuck at the optical fiber end faces or caused fitting failures. This is because the gaps between the guide pins and the guide holes were very small, providing precise fitting.
The optical connector described in Literature 1, described above, is provided with the escape face lib at the end face 11a of a ferrule 11 against which another ferrule 11 is butted. The guide holes 12 are made to open at this escape face 11b to avoid an increase in butting failures and connection loss caused especially by foreign matter 21, such as dirt or dust, which gets stuck or remains after cleaning around the guide pins 14.
In Literature 1, however, no description is given regarding the production of powder caused by the friction generated when the guide pins are inserted and fitted into the guide holes. Since the guide pins and the guide holes conforming to the JIS are used in Literature 1, the production of powder caused by the friction generated by repeated connection and disconnection cannot be avoided.
To avoid an increase in connection loss caused by the production of such powder due to friction, it is necessary to frequently clean the end faces of the ferrules, for example. However, frequent cleaning is troublesome, and asking ordinary users to perform such cleaning is not appropriate for optical connectors designed for commercial use. It is difficult to stipulate that cleaning is a condition of use.